What is the nearest beach to Lake Chapala?

As the crow flies, the nearest beaches to Chapala will be down by Manzanillo (180 miles from Ajijic on the north shore of Chapala), though as this is Mexico's busiest port, not sure how clean the water/sand will be. Manzanillo has a number of oceanfront resorts and hotels, plus some decent snorkeling/swimming in Santiago Bay a few miles north of town. For better beach life, I'm inclined to suggest you head west to Puerto Vallarta, which is about 200 miles as the crow flies from Chapala area. You can get there by bus by way of the big city of Guadalajara, which is about 35 miles north of Ajijic. Ffrom there, it's about a five-hour journey by bus to PV. By all accounts, the bus lines in Mexico are really quite good. Two companies you might check out for services between Guadalajara and Puerto Vallarta (as well as Manzanillo) are ETN (http://www.etn.com.mx) and Primera Plus (http://www.primeraplus.com.mx).